Earlier quoted context omitted.
I watched a good friend freak out in front of me on a bad trip. Almost thirty years later he's still not the same and needs antipsychotic medication to function. This kind of thing isn't common but it can definitely happen.
It's entirely possible that LSD uncovered or accentuated an underlying flaw in your friend's psyche...
Even if it's true that someone has some kind of latent / dormant condition that is ultimately triggered by the LSD, then the act of taking the LSD itself was the catalyst, and the person would have been far better off not ever having taken the drug.
The drug is illegal, and the argument growing up was that the "government was suppressing free thought" or whatever nonsense was being pushed, but the reality is that such a drug is dangerous and absolutely does hurt people. Whether connected to a predisposition of mental illness or not, it's not a hard connection and people should be extra cautious when considering whether to engage in such behavior.